Guanine photophysics

Sobolewski AL, Domcke W (2004) Ab initio studies on the photophysics of the guanine-cytosine base pair. Phys Chem Chem Phys 6 2763... 

A few chapters of the current volume describe different state-of-the-art experimental techniques used to unravel photophysical and photochemical properties of complex molecular systems. These chapters are especially tailored for the scholarly description of electronic excited state properties of nucleic acid bases and related species predicting different tautomeric distributions and possible nonra-diative deactivation processes. It is interesting to note that guanine provides particularly challenging case to discuss. Recent theoretical and experimental investigations show the existence of relatively significantly less stable imino tautomers in the... 

Keywords Guanine, IR Spectroscopy, Photophysics, UV Spectroscopy, Tautomers... 

Figure 13-8. Relevant schematic potential energy curves for the near UV photophysics of the most stable tautomers of guanine. The region of the first singlet tht excited state surface accessible by Franck-Condon excitation is indicated in bold. Excited state internal conversion through a conical intersection (Cl) with S0 is illustrated by curved arrows. Vertical arrows indicate fluorescence emission. The eventual role of excited nir singlet states cannot be ruled out, especially at high energy excess in the excited state (see text)...

Serrano-Andres, L., Merchan, M.> 8c Borin, A. C. (2008). A three-state model for the photophysics of guanine. Journal of the American Chemical Society, 130, 2473-2484. 

A novel method for improving the conductivity of DNA involves close association or even incorporation of divalent metal ions such as Zn, Ni, and Co into the hehx at pH>8.5 to form metallated DNA (M-DNA). Other divalent metals such as Mg + and Ca " do not form M-DNA. In photophysical studies using ds-DNA where one strand is labeled with a fluorescein fluorophore and the complementary strand carries a rhodamine quencher, the fluorescein fluorescence is quenched only under conditions where M-DNA forms. M-DNA is an efficient conductor of electrons over distances as long as 500 basepairs and possibly as long as several micrometers. It was proposed that in M-DNA the Zn cations replace the imino protons of every thymine and guanine in addition to saturating the backbone phosphates as do other cations such as Mg (Scheme 6). Importantly, M-DNA... 

Studies on the Photophysics of the Guanine-Cytosine Base Pair. 

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